1. Field of the Invention
The present invention relates to write power control methods and write power control apparatuses in drive technologies that record information on optical disks such as CD-Rs, CD-RWs, DVD+RWs, and DVD+Rs.
2. Description of the Related Art
Information is recorded on recordable (write once) and rewritable optical disks by applying thereon a dye-based phase change recording material, for example, forming recording marks by irradiating a laser beam while following a groove, and irradiating the laser beam of an erase power so as to erase the recording marks that are previously recorded. In order to stably form recording marks and recording spaces on an optical disk under a certain condition, it is necessary to control the drive current of a LD (laser diode) so that constant laser power is always obtained in accordance with information.
Regarding improving the methods, power control methods in optical disk recording include a method of holding each of peak and bottom values of an optical output pulse, calculating a recording base value based on the held peak and bottom values and the level ratio of the recording base value with respect to predetermined peak and bottom values, and controlling the optical output pulse such that the peak value, bottom value, and recording base value approach respective target values (for example, refer to Japanese Laid-Open Patent Application No. 2000-30276).
Although the method described above is effective for a single pulse waveform, the method cannot be applied to a multi-pulse waveform. The recording waveform of a laser beam is a multi-pulse waveform of which signal level, having a peak power, an erase power, and a bottom power, is defined by a predetermined switching timing so that best recording quality is achieved. However, with conventional methods it has been impossible to control a multi-pulse to maintain optimum write power since it is difficult to measure a multi-pulse.